1. Field of the Invention
The present invention relates generally to hip prostheses and more specifically to an interlocking reverse hip prosthesis allowing increased range of motion and stability during excessive ranges of motion.
2. Description of the Prior Art
It can be appreciated that several hip implants have been in use for years. Typically, a conventional hip implant comprises a femoral component having an articulating femoral ball attached to a stem, which is inserted into the medullary canal of the femur after preparation and reaming using appropriate reamers by the operating surgeon. Said stem can be secured with bone cement or press fit. An acetabular component or socket having the shape of a cup is inserted into the acetabular cavity after preparation and appropriate reaming and secured with cancellous screws through holes in the implant, bone cement or press fit or a combination thereof.
The acetabular cup will then receive a lining made of high-density polyethylene or ceramic. Said lining will be secured into the acetabular cup by a press fit mechanism. The main problem with conventional hip implants is the instability of the prosthesis at the extreme ranges of motion thereby allowing the femoral ball to dislodge and dislocate. Prior art teaches constrained and preassembled ball and socket devices or a device wherein the ball and socket members are implanted separately whereupon the ball element is forced into a resilient opening in the socket and thereafter held in place by the resilient material. Other constrained acetabular sockets include a locking ring such as the one described by Albertorio et al. U.S. Pat. No. 6,527,808. In the case of socket elements having a retaining ring, the ball member is forcefully inserted into the socket after the two elements are implanted. This constitutes a weak link where forces exerted on the prosthesis by ambulatory motion may exceed the forces used to assemble the implant thereby causing the ball to be separated from the socket.
While these devices may be suitable for the particular purpose to which they address, they are not suitable for providing an interlocking mechanism as in the reverse hip implant design of the present invention, which by the very nature of its design allows increased range of motion and increased stability at extreme ranges of motion thereby reducing the risk of dislocation.
In these respects, the interlocking reverse hip prosthesis according to the present invention substantially departs from the conventional concept and design of the prior art, and in so doing provides an apparatus primarily developed for the purpose of reducing the risk of dislocation of hip implants at extreme ranges of motion. Furthermore, since the articulating surfaces of the two components are fully in contact 100% of the time, it is clear that this will improve the weight distribution and decrease the wear of the surfaces in contact and reduce the number of wear particles released in the joint. The later, being very detrimental to the proper function of the joint.